Finned recuperator tubes and method of manufacture



2 Sheets-Sheet l Nov. 22, 1960 R. c. WHITNEY FINNED RECUPERATOR TUBES AND METHOD 0F MANUFACTURE med July 1e, 195e Hfs A r rom/.sv

Nov. 22, 1960 R. c. WHITNEY v2,960,746

FINNED RECUPERATOR TUBES AND METHOD OF MANUFACTURE Filed July 1e, 1956 2 sheets-sneer 2 2 INVENTOR.

L/5 RA YMaA/a CHAR Les WH/ rue' Y BY Eb 9. 4 VM H/s A rroeA/s Y United States Patent* FINNED RECUPERATOR TUBES AND METHOD OF MANUFACTURE Raymond Charles Whitney, Mount Lebanon, Pa., assiguor, by mesne assignments, to Textron Inc., Providence, RJ., a corporation of Rhode Island Filed July 16, 1956, Ser. No. 598,065

2 Claims. (Cl. 25-156) This invention relates generally to industrial heat exchangers, known as recuperators, and more particularly to a recuperator tube tile structure that conducts the hot gases from the furnace chamber through the recuperator to a stack to effect a heat exchange.

This invention is directed to a tubular tile structure that combines large surface area for efficient transfer of heat and physical strength and is an improvement over U.S. Patent 2,733,908. The principal object of this invention is the provision of a tile structure of this character than can withstand uneven expansion under extreme temperatures.

One of the most popular recuperator tile structures is the octagonal tile which has on its interior walls longitudinally extending ribs for providing increased area and heat transference and added strength with less wall cross section. The exterior walls of this iiue tube has annular ribs which not only add strength but provide additional surface for treating the air that passes laterally across the exterior of the tube.

This type tile structure introduced a new and very serious problem of uneven expansion in the tile structure. High temperature waste gases from the furnace are directed through the interior portion of the tile and the longitudinal ribs absorb the heat while the annular exterior ribs of the tile transfer this absorbed heat to the air passing around the outer surfaces of the tile. 'Ihis produces expansion in the interior surfaces creating internal stress in the annular ribs which being relatively cool resist this expansion causing the tile to crack.

This invention provides one or more notches in each annular rib to relieve these internal stresses. Each notch is placed opposite an interior -rib to allow expansion of the tile body without creating stresses in the annular ribs. Thus the advantages of large surface area in conjunction with efficient heat transfer and tile structure strength can be provided regardless of the differences in the temperatures of inner and outer tile surfaces.

It has been discovered that the depth of the exterior notches should extend through the major portion of the thickness of the annular rib. To prevent strains during drying and firing, these notches should either be molded into the annular ribs or cut into the ribs `after the tile is removed from the mold and when in a leathery state.

While tiles of circular tand octagonal cross section were discussed here, it can be easily seen that the principle of this invention can be applied to any cross-sectional recuperator tile such as triangular, square, hexagonal or other shapes.

Other objects and advantages appear hereinafter in the following description and claims.

The accompanying drawings show for the purpose of exempliiication, without limiting the invention or claims thereto, certain practical embodiments of the invention wherein:

Fig. 1 is a view in vertical section of recuperator tile structures as they appear in a portion of a refractory chamber, parts of which are broken away.

Fig. 2 is a view partly in side elevation and partly in section of the octagonal tubular tile structure comprising this invention. Y

Fig. 3 is a view in top elevation of Fig. 1.

Fig. 4 is an enlarged view of one of the longitudinal ribs and its corresponding notch of Fig. 3.

Fig. 5 is a view in top elevation showing a circular tile structure.

Referring to Fig. 1 the recuperator chamber 1 has the side walls 2. High temperature waste gases enter through the passage 3 at the top of the chamber 1. Tubular-tile sections 4 which are supported at the bottom of the chamber 1 by the bridge wall 5 make up the horizontal courses of the ceramic. The bridge wall 5 has openings 6 with which the sections 4 are aligned. Vertical flue tiles 7 are stepped into sockets of the sections 4 and are thus aligned therewith for the purpose of conducting the waste gases down through the chamber 1. The horizontal courses are completed by the block 8 which fits between the sections 4.

The air to be heated in the chamber 1 enters through a passage 10 and is circulated laterally back and forth across the chamber between the horizontal tile sections 4 and it travels upward through openings where selected blocks 3 have been removed in the horizontal courses. After the air passes through each horizontal passage it passes out of the recuperator chamber at the upper right hand side of the chamber as indicated at 9 on its way to the burner.

Referring to Figs. 2, 3 and 4 the octagonal flue tile 7 has longitudinal n'bs 11 on every other corner of its inner surface or bore to project into the direct iioW of waste gases for absorbing and distributing the gases as Well as the heat therefrom. These ribs add strength to the tile by increasing the cross-sectional area of the tile and permit its intermediate wall to be reduced to a minimum. This feature of the tile allows maximum heat transfer with no loss in the strength of the tile.

The external portion of the flue tile 7 is provided with a series of annular ribs 12 to increase the surface exposed to the air traveling transversely for more eilicient heat transfer. Each exterior annular rib 12 has `at least one notch 13 positioned opposite to a longitudinal rib 11. There may be as many notches 13 as there are ribs. The area of the notches 13 in the exterior annular ribs 12 falls or lies substantially within the area of the longitudinal interior ribs 11. That is the area of the base portion of each longitudinal interior rib 11 overlies or extends over an area in which the widest portion of each notch 13 would lie or extend. The notches 13 thus interrupt the continuous band of these annular ribs 12 and permit expansion of the tube. The continuous band would allow strains to build up and cause the tube to crack during drying, burning or use. One or more notches thus eliminates any cracking as these strains are relieved. Yet the interrupted rib functions to perform its work. These strains are believed to be set up due to the diiference between the interior and exterior tile temperatures of these tile structures.

The interior longitudinal ribs 11 not only help direct the ow of waste gas but are placed in the bore opposite the notches 13 in the annular ribs 12 to give added strength to that portion of the tile that has been notched. It is preferable to place the notches 13 opposite the longitudinal ribs 11 which are positioned in the angles of octagon tile structures such as disclosed.

The tile structure shown in Fig. 5 is similar to that of Fig.. 3 except that it is circular instead of octagonal. Here as before the inner longitudinal ribs 14 are positioned opposite the notches 15 in the exterior annular ribs 16.

Only two denite cross-sectional shapes are shown here Patented Nov.

because they are the most prominent tiles used in the art. It is understood that the invention disclosed here may be applied to any size or shape of refractory flue tile.

I claim:

1. The method of making a refractory tubular heat transfer tube having on its interior wall spaced longitudinal ribs and on its exterior wall spaced annular ribs comprising the steps of casting the refractory member in a mold, drying the cast refractory member in the mold to a leathery state, removing the cast article from the mold when in a leathery state, relieving stress on the exterior annular ribs at spaced points by cutting said annular ribs when in a leathery state at points opposite the interior longitudinal ribs to form notches extending over an area falling substantially within the projected `area of said in- 15 2,733,908

References Cited in the le of this patent UNITED STATES PATENTS 1,658,025 Alexander Feb. 7, 1928 1,983,466 Kline Dec. 4, 1934 2,726,433 Skunda Dec. 13, 1955 Graham Feb. 7, 1956 

